System for broad spectrum drug detection

ABSTRACT

Biological fluid test samples are analyzed for a broad spectrum of drugs, including benzodiazepines, amphetamines, tricyclic antidepressants and opiates, in a single isocratic analysis using a chromatographic column system containing three analytical columns--an anion exchange column, a reversed phase column and a cation exchange column. A pre-column is also included to purge the sample of salts, proteins, peptides and hydrophilic anions. Carrier liquids containing acetonitrile at various strengths are used for distribution of the various drugs among the columns, elution of the drugs from the columns, and column purging and conditioning. The system readily lends itself to automation, automatic periodic sampling, and component identification and quantification.

This is a division of application Ser. No. 07/225,108 filed July 27,1988 now U.S. Pat. No. 5,057,437.

BACKGROUND OF THE INVENTION

This invention relates to analytical systems and methods for biologicalfluids such as serum and urine. In particular, this invention relates tochromatographic systems for multiple drug analyses in biological fluids.

A wide range of analytical methods are known for the detection of toxicdrugs in serum or urine. The most common techniques are those involvingimmunological interactions and those involving chromatographicseparation. Immunological techniques directed at single species canprovide highly accurate information regarding the presence and amount ofthe species in question. When a single immunological assay is used formultiple drug detection, it will generally detect only drugs of aparticular class, and will not provide identification of the specificdrugs which are present or their concentrations. Chromatographictechniques, including thin-layer chromatography, high performance liquidchromatography and gas chromatography, may permit detection of amultitude of drugs at the same time, but generally require extensivesample preparation and a total analysis time of 1-2 hours. Neitherimmunological nor chromatographic techniques as presently known areuseful for rapidly analyzing wide ranges of drugs.

SUMMARY OF THE INVENTION

The present invention provides a chromatographic system and method whichcombines several unique features permitting a broad spectrum druganalysis by isocratic separation in an unusually short period of time.

Among the unique features of the invention are a distinct combinationand arrangement of analytical columns, notably an anion exchange column,a reversed phase column, and a cation exchange column arrangedsequentially in that order. The invention further provides the uniquecombination of these analytical columns with a pre-column. Samples to beanalyzed are passed initially through the pre-column to be purged ofcomponents not sought to be detected in the analysis. Still further, theinvention provides an automated system which combines detection andscanning elements with a library of known spectra and retention times,to identify and quantify each component as it emerges from the columnsystem fully separated from the other drugs originally present in thetest sample. Still further, the invention provides a system whichcombines column reconditioning features with its chromatographicfunctions so that portions of the system may be reconditioned orregenerated for subsequent test samples while other portions of thesystem are in use performing the separation of a sample alreadyinjected. The invention further provides for the automatic injection ofa multitude of test samples in sequence, with full system regenerationand conditioning in between each sample.

By virtue of these unique features, the invention provides for theanalysis of any liquid test sample to identify and quantify a largemajority of the several hundred most frequently prescribed drugs, aswell as all drugs commonly analyzed by liquid chromatography. Inparticular, the system provides a highly specific separation anddetection of four classes of basic drugs --benzodiazepines,amphetamines, tricyclic antidepressants and opiates--while groupingthese drugs according to class. The system further provides for theseparation and detection of additional drugs of various types, includingantihistamines, phenothiazines and barbiturates. As indicated above, thesystem lends itself well to automation, and as a result, full analysescan be obtained unattended in an unusually short period oftime--substantially less than 1 hour, and in many cases on the order of15 minutes.

Further unique and unusual features of the invention, together withfurther advantages and utilities, will be apparent from the descriptionwhich follows.

BRIEF DESCRIPTION OF THE DRAWING

The attached FIGURE is a block flow diagram of a drug detection systemin accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

The separation media used in the present invention are placed in acolumn arrangement in such a manner that separations of certain classesof drugs are performed primarily on a single column. In particular, thesystem is arranged such that the anion exchange medium selectivelyretains hydrophobic anions and a major portion of neutral compounds,while the separation of benzodiazepines (and other weak bases) andhydrophobic bases and neutrals occurs on the reversed phase column. Thecation exchange column provides for the separation of all basiccompounds, including further separation of those separated on thereversed phase column.

To further categorize these columns and how they are used, the anionexchange column is selected and used in such a manner that it causessubstantially no retention of either bases or very hydrophilic neutralcompounds, although a slight retention of weak bases (benzodiazepines)is permissible. The separation of barbiturates and other weak acidsoccurs on this column.

The reversed phase column is selected and used in such a manner as tocause substantially no retention of hydrophilic bases, barbiturates orother anions including those which may have passed through the anionexchange medium without retention.

Likewise, the cation exchange column is selected and used in such amanner that there is substantially no retention of anions andbarbiturates. A slight retention of neutral compounds is permissible inthis column.

The anion exchange medium is preferably a polymeric resin havingquaternary ammonium functional sites. A particularly effective polymeris styrene-divinylbenzene, and the functional sites are preferablytetra(lower alkyl) ammonium moieties. A product which is particularlyeffective and commercially available as of the filing date of thisspecification is AMINEX® A-28 resin, supplied by Bio-Rad Laboratories,Hercules, Calif., which is an HPLC grade strongly basic anion exchangeresin, with tetramethylammonium functional groups on an 8% cross-linkedstyrene-divinylbenzene matrix, with an average particle size of about 11microns.

The reversed phase column may be a derivatized silica, preferably onebearing alkyl functional groups. Alkyl groups of choice are thosecontaining alkyl chains of 6 carbon atoms or more, preferably from about6 to about 18. In particularly preferred embodiments the functionalgroups are attached by bonding the silica to a dimethylalkylsilane, inwhich the alkyl group is that referred to above. Silicas of thisdescription are readily commercially available. In further preferredembodiments, the carbon loading of the silica, i.e., the carbon atomcontent in weight percent, ranges from about 6% to about 12%. with about8% to about 10% especially preferred. A commercially available productwhich has been found to be effective is MOS-HYPERSIL®, adimethyloctylsilane bonded to silica with a carbon loading of 9%.obtained from Shandon Scientific Ltd., distributed by KeystoneScientific, State College, Pa. The average particle size isapproximately 5 microns and average pore size is approximately 120Angstroms. For bonded silicas in general for this application, poresizes of 50 to 120 Angstroms may be used.

A typical cation exchange medium is underivatized silica, widelyavailable commercially. One example of a commercial product effectivefor this medium is ADSORBOSPHERE®, available from Alltech Associates,Deerfield, Ill., consisting of an underivatized silica with an averageparticle size of 5 microns, a pore size ranging from 50 to 80 Angstroms,and a surface area exceeding 350 m² /g.

By selection of the lengths of each of these columns, one can minimizeor substantially eliminate interference between emerging peaks, andminimize the analysis time as well. In general, and particularly withthe preferred column packings described above, minimal peak interferenceis achieved with an anion exchange column ranging from about 10 mm toabout 30 mm in length, a reversed phase column of about 10 mm to about50 mm in length, and a cation exchange column of about 100 mm to about250 mm in length.

The precolumn may be a polymeric resin of hydrophobic character. Apreferred example is styrene-divinylbenzene, although other resins ofsimilar character may be used. Resins of this type are widely availablecommercially, one example being a product designated PRP-1 a hydrophobicstyrene-divinylbenzene copolymer having a particle size of 12-20microns, available from Hamilton Co., Reno, Nev. Typical column lengthsrange from about 10 mm to about 30 mm.

Test samples may be applied to the precolumn by a buffer solution havinga pH of 7.5 or greater, preferably from about 7.5 to about 9.0. Oneexample of such a buffer system is a 0.1% aqueous solution of potassiumborate with a pH of approximately 8.0. This buffer solution may be usedas a carrier solution to apply the samples to the column, and also as apurging solution to purge the column once the sample is applied, toremove from the sample those species whose detection by the system isnot desired. This may be achieved by passing excess buffer solutionthrough the sample-impregnated column, preferably in both directions.Species removed include inorganic salts, proteins, peptides andhydrophilic anions.

For chromatographic separations in the analytical columns a carrierliquid containing acetonitrile is used as the mobile phase. Theacetonitrile content may vary, and will generally fall within the rangeof about 10% to about 50% by volume. Higher acetonitrile concentrationswithin this range are effective to move components through the columnsmore rapidly than lower concentrations. For example, concentrations ofabout 40% by volume or above may be used to dislodge the components fromthe precolumn after the purging of unwanted species has been completed.Concentrations on the order of 35%, 30% and lower may likewise be usedon the analytical columns to separate the drugs within each of thevarious classes. Carrier liquids similar to these but with acetonitrileconcentrations higher than the above-indicated range are effective aswash solutions to recondition the columns after use and to therebyprepare them for the next sample.

Preferred carrier liquids contain additional agents for controlling theretention and/or selectivity of certain drug classes on particularcolumns, either to enhance separation or to shorten elution times. Inparticular, long chain alkylamines, preferably those having carbonchains of 6 carbons or greater, may be used to accelerate the elution ofcertain classes such as tricyclic antidepressants from the reversedphase column. A particularly effective example is dimethyl octyl amine.The concentration of this additive may vary, but will generally fallwithin the range of about 0.001% to about 0.05% (volume basis), withpreferred amount within the range of about 30 to about 300 microlitersper liter of carrier liquid.

Likewise, retention time and selectivity on the cation exchange columnmay be controlled by inclusion of a quaternary amine in the carrierliquid. Again, concentrations may vary, although the amount willgenerally fall within the range of about 0.002M to about 0.05M. Typicalquaternary amines are tetraalkylammonium hydroxides and halides.Examples are tetrabutylammonium hydroxide, tetraethylammonium hydroxide,and tetramethylammonium chloride. In preferred embodiments, theconcentration ranges from about 0.1 to about 2.0 grams per liter ofcarrier liquid.

The carrier liquid also preferably includes a water-soluble organicsolvent combined with an aqueous buffer solution. The pH is preferablyfrom about 6.0 to about 7.5.

A convenient way of varying the acetonitrile content is by the use ofstock solutions and a mixing device for combining the stock solutions incontrolled but variable proportions. For example, a combination of twostock liquids may be used, the first being primarily acetonitrile, atleast about 75% by volume, preferably 100%, and the second containingall of the other components, including the long chain alkylamine, thequaternary amine, the buffer and the solvent. In preferred embodiments,the alkylamine will be present in the second solution at a concentrationof about 0.001% to about 0.05%, the quaternary amine will be present ata concentration of about 0.002M to about 0.05M, and the solvent at about20% to about 60% by volume, the pH being from about 6.0 to about 7.5.The buffer is preferably within the range of about 0.005 to about 0.1M.

The attached FIGURE is a block diagram illustrating an automatedanalytical system in accordance with the present invention, as anexample embodying the principles described above. The following is adescription of this system, including system parameters and operatingconditions employed in a prototype constructed in accordance with thissystem.

The three primary chromatographic columns of the system are contained ina temperature-controlled housing 11 which is maintained at a constanttemperature, generally within the range of about 40°-45° C. The threecolumns are an anion exchange column 12, which contains a packing ofstyrene-divinylbenzene copolymer with tetramethylammonium functionalgroups. The average particle size is 11 microns, and the column 10 mm inlength and 3.2 mm internal diameter. It is expected that similar columnswith lengths up to 30 mm and internal diameter up to 4.6 mm will yieldsimilar results. Downstream of the anion exchange column 12 is thereversed phase column, which is packed with an octyl-bonded silica whichhas a carbon loading of 9%, an average particle size of about 5 micronsand an average pore size of about 120 Angstroms. The column is 20 mm inlength and 3.2 mm internal diameter. It is expected that similar resultswill be obtained by varying the length and diameter within 50%.

The furthest column downstream is the cation exchange column 14, packedwith underivatized silica having an average particle size of about 5microns, an average pore diameter of 50-80 Angstroms, and a surface areaexceeding 350 m² /g. The column is 150 mm in length and 4.0 mm ininternal diameter, both variable within 20%.

Upstream of these columns is the precolumn 15, of length 15 mm andinternal diameter 2.1 mm, packed with a hydrophobicstyrene-divinylbenzene packing, with an average particle size rangingfrom about 12 to about 20 microns.

The system contains a series of liquid reservoirs 18 which supply thevarious solvents and carrier liquids to the system. Three of thereservoirs 19, 20, 21 feed a common pump 22, while the fourth reservoir23 feeds a separate pump 24. The separation of feeds between two pumpspermits the flow of two different liquid solutions into differentportions of the system at the same time. A sample selection valve 25provides for variable flow selection among the transfer lines leadingfrom the three reservoirs 19. 20. 21 to the pump 22, so that solutionsfrom the three reservoirs can be combined in variable proportions into asingle stream. This valve may be incorporated into the pump 22 itself,such as for example a low-pressure ternary gradient pump. The secondpump 24 will generally be an isocratic pump.

In the prototype system, the first liquid reservoir 19 contains theapplication or sample purging buffer. The second and third liquidreservoirs 20, 21 contain liquids which include the components of thecarrier solution distributed between them such that, when these liquidsare combined in certain proportions, carrier solutions of the desiredstrengths are obtained. The fourth liquid reservoir 23 contains a fullyconstituted carrier liquid of a specified strength which can be pumpedthrough the isocratic pump 24 at the same time that a solution drawnfrom one or more of the first three reservoirs 19. 20. 21 is pumpedthrough the gradient pump 22.

Test samples to be analyzed enter the system through an automatedsampling device 28, which draws precisely measured aliquots (0.5 mL) ofeach test sample and injects them into the flowing liquid streamemerging from the pump 22 at preselected intervals. Conventionalequipment designed for serial sample injection is commercially availableand may be used.

The arrangement of liquid flows to the various columns, and theconnection and disconnection between the columns is achieved by an 8-wayvalve 30 and two 4-way valves 31, 32. These are conventional pieces ofequipment commercially available. Each is shown in one of two positions,the other achieved by rotating in either direction through an arc equalto the distance between adjacent ports. The 8-way valve 1 is arranged topass fluids through the precolumn 15 in either direction, and to directthe column effluent either to waste 33 or to an input port on the 4-wayvalve 31 immediately downstream. The latter is likewise- arranged toreceive fluid streams from the two input lines driven respectively bythe two pumps 22, 24, and to direct one of these to the analyticalcolumn housing 11 and the other to the second 4-way valve 32 which isinterposed between the anion exchange column 12 and the reversed phasecolumn 13. The second 4-way valve 32 in turn receives fluid flow fromthe anion exchange column 12 and the first 4-way valve 31, and directsone of these to the reversed phase column 13 and the other to waste 34.

The stream emerging from the silica column 14 contains the drugs fullyseparated and ready for detection. The stream passes through a scanningUV detector 35. This unit consists of conventional instrumentation whichdetects the peaks as they emerge using standard chromatographicdetection methods, and further performs a UV absorptivity scan of eachpeak preferably at multiple points on the peak, such as the midpoints ofthe leading and trailing sides as well as the apex of the peak itself.Fluids which have passed through the detector are then passed to waste36.

The information obtained in the detector 35 is monitored and processedby a computer/monitor unit 37. This unit contains a memory library ofretention times and UV absorptivity scans for known drugs, and comparesthe data received from the detector 35 with the library information as ameans of establishing the identity of each drug as it passes through thedetector 35. The computer/monitor 37 further integrates the peaks toprovide information on the relative amounts of the drugs present in thesample. Thus, for each emerging drug, the system determines its identity(by UV scan and retention time) and its quantity (by peak integration).This information is then transmitted to a printer 38, which provides afull printed analysis of UV-absorbing drugs which have reached thedetector.

At the center of the system, coordinating the entire sequence ofoperations is a system controller 39 which controls the sample selectionvalve 25, and the computer/monitor 37. The controller 39,computer/monitor 37, printer 38 and detector 35 are conventionalequipment commercially available and used in the industry for the sameor similar functions.

The following is a sequence of events used for drug analysis of serum orurine on the above-described prototype. In this description:

    ______________________________________                                        column 1 is the PRP-1 pre-column (element 15 in the drawing)                  column 2 is the AMINEX phase column (element 12)                              column 3 is the reversed phase column (element 13)                            column 4 is the silica column (element 14)                                    solvent A is 0.1% borate buffer, pH 8.0                                       solvent B is a mixture of:                                                     5 mL 1 M KH.sub.2 PO.sub.4                                                   150 μL dimethyloctylamine                                                  275 mg tetramethylammonium chloride                                           645 mL water                                                                  pH adjusted to 6.75 ± 0.02 with H.sub.3 PO.sub.4 or KOH                    solvent C is HPLC grade acetonitrile                                          valve 1 is the 8-way valve (element 30)                                       valve 2 is the first 4-way valve (element 31)                                 valve 3 is the second 4-way valve (element 32)                                ______________________________________                                    

    ______________________________________                                        Duration                                                                              Flow Conditions Event Description                                     ______________________________________                                        Step 1  Column 1 rinsed in                                                                            Column 1                                              0.5 minute                                                                            100% C at 4.0 mL/min.                                                                         reactivated to                                                Columns 2, 3 and 4 in                                                                         prepare for new                                               65% B, 35% C at 1.0                                                                           sample.                                                       mL/min. Sample pickup                                                         in progress.                                                          Step 2  Column 1 rinsed in                                                                            Column 1 rinsed                                       0.5 minute                                                                            100% A at 4.0 mL/min.                                                                         with buffer to                                                Columns 2, 3 and 4 in                                                                         prepare for new                                               65% B, 35% C at 1.0                                                                           sample.                                                       mL/min. Sample pickup                                                         in progress.                                                          Step 3  Sample pickup   Sample transferred                                    0.1 minute                                                                            completed. Otherwise                                                                          to column 1.                                                  same conditions as                                                            step 2.                                                               Step 4  Conditions identical                                                                          Column 1 rinsed in                                    0.5 minute                                                                            to Step 3.      forward direction.                                    Step 5  Valve 1 reversed.                                                                             Column 1 rinsed in                                    1.5 minutes                                                                           Conditions otherwise                                                                          reverse direction.                                            identical to step 3.                                                  Step 6  Valve 2 switched to                                                                           High strength                                         0.2 minute                                                                            connect all four col-                                                                         mobile phase used                                             umns. 60% B, 40% C at                                                                         to dislodge drugs                                             1.0 mL/min passed                                                                             from column 1.                                                through.                                                              Step 7  70% B, 30% C at 1.0                                                                           Low strength mobile                                   0.6 minute                                                                            mL/min.         phase used to                                                                 continue transfer                                                             of drugs,                                                                     concentrating drugs                                                           at heads of                                                                   analytical columns.                                   Step 8  65% B, 35% C at 1.0                                                                           Fastest drugs have                                    0.1 minute                                                                            mL/min.         moved from column                                                             2 to column 3;                                                                slowest drugs                                                                 moving from column                                                            1 to column 2.                                        Step 9  Valve 2 switched to                                                                           Remaining drugs                                       0.5 minute                                                                            disconnect columns 1                                                                          moving through                                                and 2. 30% B, 70% C                                                                           columns 2 and 3 to                                            passed through column                                                                         column 4. Rinse of                                            1 at 1 mL/min; 65 % B,                                                                        column 1 begins.                                              35% C passed through                                                          columns 2, 3 and 4 at                                                         1.0 mL/min.                                                           Step 10 Valves 2 and 3  All drugs have                                        5.2 minutes                                                                           switched to connect                                                                           passed through                                                columns 1 and 2 and                                                                           columns 1 and 2,                                              disconnect columns 3                                                                          which are now being                                           and 4. 1 and 2  rinsed                                                        receive 30% B, 70% C                                                          at 1.0 mL/min; 3 and 4                                                        receives 65% B, 35% C                                                         at 1.0 mL/min.                                                        Step 11 65% B, 35% C passed                                                                           Columns 1 and 2                                       5.2 minutes                                                                           through columns 1 and                                                                         being reequilibrated                                          2 at 1.0 mL/min;                                                                              in mobile phase.                                              columns 3 and 4 flow                                                          continued as in step 10.                                              Step 12 All flow rates lowered                                                                        End of run.                                           .05 minute                                                                            to 0.1 mL/min.                                                        ______________________________________                                         Note: Data analysis and printing of the report for each sample occurs         during steps 1 through 7 of the subsequent sample.                       

The following is a representative list of drugs for which a sample ofserum or urine may be analyzed by use of the scheme described above.This list is merely illustrative and is not intended to becomprehensive.

DETECTABLE DRUGS

    ______________________________________                                        DETECTABLE DRUGS                                                              Drug (in alphabetical order)                                                                   Column(s) Where Retained                                     ______________________________________                                        alprazolam       reversed phase                                               amitriptyline    reversed phase, silica                                       amoxapine        reversed phase, silica                                       amphetamine      silica                                                       benzoylecgonine  silica                                                       butalbital       anion exchange                                               chlordiazepoxide reversed phase                                               chlorpheniramine silica                                                       cimetidine       silica                                                       cocaine          silica                                                       codeine          silica                                                       desalkylflurazepam                                                                             reversed phase                                               desipramine      reversed phase, silica                                       diazepam         reversed phase                                               diphenhydramine  reversed phase, silica                                       doxepin          reversed phase, silica                                       ephedrine        silica                                                       ethclorvynol     reversed phase                                               glutethimide     anion exchange                                               imipramine       reversed phase, silica                                       lidocaine        silica                                                       lorazepam        reversed phase                                               loxapine         reversed phase, silica                                       maprotiline      reversed phase, silica                                       meperidine       silica                                                       methadone        silica                                                       methamphetamine  silica                                                       methaqualone     reversed phase                                               morphine         silica                                                       oxazepam         anion exchange, reversed phase                               pentazocine      silica                                                       phencyclidine    silica                                                       phenobarbital    anion exchange                                               phentermine      silica                                                       phenylpropanolamine                                                                            silica                                                       phenytoin        anion exchange, reversed phase                               propoxyphene     silica                                                       pyrilamine       silica                                                       quinidine        reversed phase, silica                                       secobarbital     anion exchange                                               thioridazine     reversed phase, silica                                       tripelennamine   silica                                                       ______________________________________                                    

The foregoing is offered primarily for purposes of illustration. It willbe readily apparent to those skilled in the art that numerousvariations, modifications, and substitutions may be made among thevarious procedures, materials, and other elements of the systemdescribed above without departing from the spirit and scope of theinvention.

What is claimed is:
 1. A system for analyzing a biological sample forthe presence of drugs in the form of anions, bases and neutralcompounds, said system comprising:(a) means for purging said sample ofinorganic salts and proteins; (b) a chromatographic column combinationcomprising, in the sequence given:(i) an anion exchange medium; (ii) areversed phase medium; (iii) a cation exchange medium; and (c) a carrierliquid; and (d) means for identifying said drugs as they emerge fromsaid chromatographic column combination; said carrier liquid selected,and said chromatographic column combination arranged, to promote theselective retention of hydrophobic anions and neutral compounds otherthan hydrophilic neutral compounds, substantially no retention of bases,and the chromatographic separation of weak acids from each other on saidanion exchange medium; the chromatographic separation of weak bases,hydrophobic bases, and neutral compounds, with substantially noretention of hydrophilic bases, barbiturates and anions on said reversedphase medium; and the chromatographic separation of bases from eachother on said cation exchange medium, with substantially no retention ofanions and barbiturates.
 2. A system in accordance with claim 1 in whichsaid purging means is comprised of a hydrophobic styrene-divinylbenzenecopolymer resin.
 3. A system in accordance with claim 2 in which saidpurging means further comprises an aqueous buffer solution at a pH of atleast about 7.5.
 4. A system in accordance with claim 2 in which saidpurging means further comprises an aqueous buffer solution at a pH of atabout 7.5 to about 9.0.
 5. A system in accordance with claim 1 in whichsaid anion exchange medium is a packed column of from about 10 mm toabout 30 mm in length, said reversed phase medium is a packed column offrom about 10 mm to about 50 mm in length, and said cation exchangemedium is a packed column of from about 100 mm to about 250 mm inlength.
 6. A system in accordance with claim 1 in which said anionexchange medium is a polymeric resin with quaternary ammonium functionalsites.
 7. A system in accordance with claim 1 in which said anionexchange medium is a styrene-divinylbenzene resin with quaternaryammonium functional sites.
 8. A system in accordance with claim 1 inwhich said anion exchange medium is a styrene-divinylbenzene resin withtetramethylammonium functional sites.
 9. A system in accordance withclaim 1 in which said reversed phase medium is a derivatized silica. 10.A system in accordance with claim 1 in which said reversed phase mediumis silica bearing alkyl functional groups.
 11. A system in accordancewith claim 1 in which said reversed phase medium is silica bearing alkylfunctional groups with a carbon content of about 6% to about 12% byweight.
 12. A system in accordance with claim 1 in which said reversedphase medium is silica bearing octyl functional groups with a carboncontent of about 8% to about 10% by weight.
 13. A system in accordancewith claim 1 in which said cation exchange medium is comprised ofsilica.
 14. A system in accordance with claim 1 in which:said purgingmeans is comprised of a hydrophobic styrene-divinylbenzene copolymerresin, said anion exchange medium is a polymeric resin with quaternaryammonium functional sites, said reversed phase medium is silica bearingalkyl functional groups with a carbon content of about 6% to about 12%by weight, and said cation exchange medium is underivatized silica. 15.A system in accordance with claim 1 in which:said purging means iscomprised of a hydrophobic styrene-divinylbenzene copolymer resin, saidanion exchange medium is a styrene-divinylbenzene resin withtetramethylammonium functional sites in a packed column of about 10 mmto about 30 mm in length: said reversed phase medium is octyl-bondedsilica with a carbon content of about 8% to about 10% by weight in apacked column of about 10 mm to about 50 mm in length and said cationexchange medium is underivatized silica in a packed column of about 100mm to about 250 mm in length.
 16. A system in accordance with claim 1 inwhich said carrier liquid contains acetonitrile at about 10% to about50% by volume.
 17. A system in accordance with claim 1 in which saidcarrier liquid contains acetonitrile at about 10% to about 50% by volumeand dimethyloctylamine at about 30 to about 300 μL per liter.
 18. Asystem in accordance with claim 1 in which said carrier liquid containsacetonitrile at about 10% to about 50% by volume, dimethyloctylamine atabout 30 to about 300 μL per liter, and a member selected from the groupconsisting of tetraalkylammonium hydroxides and halides at about 0.1 toabout 2.0 g per liter.
 19. A system in accordance with claim 1 furthercomprising:a first stock liquid containing at least about 75%acetonitrile by volume: a second stock liquid comprising an aqueousbuffer solution having dissolved therein from about 0.001% to about0.05% by volume of an alkylamine with a carbon chain of at least 6carbon atoms, from about 0.002M to about 0.05M of a quaternary amine,and from about 20% to about 60% by weight of a water-soluble organicsolvent, at a pH of from about 6.0 to about 7.5: and variable mixingmeans for combining said first and second stock solutions to form saidcarrier liquid, in a plurality of proportions to vary the concentrationof acetonitrile in said carrier liquid.
 20. A system in accordance withclaim 19 further comprising control means for controlling said variablemixing means and for directing aid carrier liquid to preselectedportions of said chromatographic column combination in a selectedsequence, to condition portions of said chromatographic columncombination while said drugs are passing through remaining portionsthereof.
 21. A system in accordance with claim 1 further comprisingmeans for automatically feeding a plurality of samples to said systemfor analysis therein at periodic intervals.
 22. A system in accordancewith claim 1 in which said identifying means comprises means forautomatically scanning each said drug emerging from said chromatographiccolumn combination to produce an absorption spectrum characteristic ofeach said drug: a library of presupplied spectra of known drugs; andmeans for automatically comparing spectra produced by said scanningmeans with said presupplied spectra to determine the identity of drugsemerging from said chromatographic column combination.
 23. A system inaccordance with claim 1 in which said identifying means comprises meansfor automatically detecting retention times of said drugs as they emergefrom said chromatographic column combination: a library of predeterminedretention times for known drugs: and means for automatically comparingretention times so detected with said predetermined retention times todetermine the identity of drugs emerging from said chromatographiccolumn combination.
 24. A system in accordance with claim 1 furthercomprising means for determining the relative amounts of said drugs insaid sample as said drugs emerge from said chromatographic columncombination.
 25. A system in accordance with claim 1 in which saididentifying means comprises:(a) means for automatically scanning eachdrug emerging from said chromatographic column combination to produce anabsorption spectrum characteristic of each said drug; and means forautomatically comparing spectra produced by said scanning means withsaid presupplied spectra; (b) means for automatically detectingretention times of said drugs as they emerge from said chromatographiccolumn combination; a library of predetermined retention times for knowndrugs; and means for automatically comparing retention times so detectedwith said predetermined retention times; and (c) peak integrating meansfor determining the relative amounts of said drugs in said sample assaid drugs emerge from said chromatographic column combination.